1. Field of the Invention
This invention relates generally to magnetic heads in disk drives, and more particularly to magnetic heads having insulator materials containing cobalt-oxide which can effectively dissipate heat from the magnetic head.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) or giant magnetoresistive (GMR) read head to form a merged head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces terminate at the ABS where first and second pole tips are defined. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces magnetic write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS fringe across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to, and a short distance (fly height) from, the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR or GMR read head.
An MR read head includes an MR sensor sandwiched between first and second non-magnetic gap layers and located at the ABS. In turn, the first and second gap layers are sandwiched between first and second shield layers. In a merged MR head, the second shield layer and the first pole piece are a common layer. The first shield layer is formed over an undercoat layer, which is in turn formed over a substrate. The MR sensor detects magnetic fields from the circular tracks of the rotating disk by a change in resistance that corresponds to the strength of the fields. A sense current is conducted through the MR sensor, where changes in resistance cause voltage changes that are received by the processing circuitry as readback signals.
On the other hand, a GMR read head includes a GMR sensor which manifests the GMR effect. In the GMR sensor, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. GMR sensors using only two layers of ferromagnetic material (e.g., nickel-iron, cobalt, or nickel-iron-cobalt) separated by a layer of nonmagnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors which manifest the SV effect. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. A GMR head is typically associated with a design in which the second shield layer and first pole piece are not a common layer. These pieces are separated by a non-magnetic material or a metal that is typically deposited using a physical vapor deposition technique or an electroplating technique.
When the disk drive is in operation, heat is produced within the magnetic head. If not effectively dissipated, the heat can cause undesirable problems in the magnetic head. For example, the maximum amplitude of a bias current which is applied to the read sensor is limited by the sensor's heat dissipation capability. This limitation imposes a constraint on the readback signal amplitude and the signal-to-noise ratio of the read sensor. Heat conduction cooling of the read sensor is strongly impeded by the use of conventional dielectric gap layers, typically made of alumina (Al2O3), which physically separate the sensor from the shield layers. The engineering of magnetic materials alone is insufficient to achieve the needed improvement in the read sensor output, especially as recording areal densities continue to increase rapidly. Another problem with heat in the magnetic head is that it may cause several layers in the head to thermally expand during write operations. The thermal expansion of these layers tends to cause mechanical protrusion which, in turn, may cause head-to-disk interface reliability problems.